Glass fibres are produced by spinning molten feed-stock to force the extrusion of fibre-forming streams of molten glass under centrifugal forces from the periphery of a spinning head. The spinning head used in this process has a circumferential extrusion rim with a spinning face surface pierced by orifices through which the molten fluid is forced.
Particularly in the case of glass, the constant flow of a high temperature thermoplastic melt through the orifices leads to corrosion and to erosion of the orifices. The extrusion orifices or holes are chosen to be of a preferred diameter in order to control the diameter of the fibres. Maintaining constant fibre diameter is a critical factor in the production of fine fibres and the production of consistently fine fibres is highly desirable. Once the extrusion holes are oversize, these objectives are not met and eventually, a worn spinning head must be replaced.
Due to the difficulties in maintaining relative evenness in the throughput of extrusion orifices and similar overall fiber-forming conditions, the extrusion rims on conventional spinning heads have been limited in their relative height (see U.S. Pat. No. 4,359,444 at column 1, lines 33-35). This prior art limitation that the height of the spinning face be kept minimal has assured that the extrusion orifices distributed over the surface of the extrusion rim are largely operating to produce fiber product with a relatively narrow fiber diameter distribution spectrum until wear of the orifices disrupts this balance.
To achieve an increase of productivity from fiberizers, a trend has developed of providing larger capacity by increasing the head diameter, and correspondingly increasing the circumferential surface area of the spinning face at the extrusion rim. However, upgrading production equipment by this means is expensive because it requires building a new environment of support peripherals for each head, designed to accommodate an increased diameter.
A need exists to permit the increase of production capacity from a fibre spinning head without significantly increasing the diameter of the head.
It is known to produce fibres using a partitioned spinning head wherein two different feed-stocks are fed to common extrusion orifices to form helical fibres. The two feeds are chosen to have differing coefficients of thermal expansion--shrink factors--so that on cooling the single fibre of binary composition naturally curls into the form of a helix. A prior art disclosure of a spinning head of this type is depicted in U.S. Pat. No. 5,482,527 issued Jan. 9, 1996.
In this reference the spinning head is partitioned to receive two separate streams of molten material, fed into the spinning head at two separate radial distances from the central axis of the head. A first stream, which is delivered at the smaller radial distance, is deposited on the bottom surface or floor of the spinning head. The second stream, which is delivered at a larger radial distance, is deposited on a mid-level, annular platform that keeps the second feed-stock separated from the first.
Both molten compositions are flung outwardly under centrifugal force towards the orifice-containing rim of the partitioned spinning head. At the rim, separated pathways formed in the head allow the two molten compositions to merge in pairs at multiple extrusion orifices to form a binary extruded filament. These filaments are directed by high velocity gas jets and gravity to fall downwardly, solidifying, as a veil. The fibres become attenuated in their diameter in the process, and break at intervals into fibre segments of acceptable lengths.
In this prior art arrangement, balanced flows of molten feed-stock are delivered to the dual-access orifices to provide a consistent ratio of delivered components to each fibre. This ratio need not be equal but, in this prior art reference, this ratio is not expected to vary over time or between orifices. No attempt is made to create distinct fibre-forming zones on the spinning face of the extrusion rim.
Another reference that premises the reception of two, distinct, but continuous feed-stocks of molten material is U.S. Pat. No. 5,582,841 to Watton et al. In this reference an annular partition wall mounted centrally above the floor of the spinner initially maintains separation between the two feed-stocks. In one embodiment the separate flows are delivered to paired extrusion outlets to form dual component fibres. Alternately, the observation is made (column 2, lines 60-65) that these flows may be kept separate in order to form single-component fibres. An objective of this reference, however, is to maintain an even distribution of mass behind all of the extrusion orifices (column 3, lines 10-12).
This arrangement is not otherwise depicted or discussed in the disclosure. Nor are the extrusion orifices from the two glass streams kept separate in non-overlapping zones.
This reference does not suggest that the glass fibre production apparatus be otherwise modified. The same supporting hardware is to be employed: two classes of glass melt, two bushings supply glass from separate forehearths, and the spinning head has intermixed extrusion orifices producing fibre at presumably similar rates into a common attenuation environment. Accordingly, the two glass streams would produce fibres, albeit of different types of glass, under common fiberizing conditions. No suggestion is made to provide a single, common supply of glass and to physically divide the single melt into separate parts that are then delivered to different fibre forming zones with different fiberizing conditions within a common spinning head.
Further references having a similar structure are U.S. Pat. Nos. 5,468,275 and 5,474,590, both to Lin et al. and U.S. Pat. No. 3,190,736 to Benner which similarly addresses the objective of evenly delivering molten material to a common set of extrusion orifices by providing multiple pathways for such material to arrive at the outside extrusion rim.
The objective of evenly distributing hot, thermoplastic feed-stock over the extrusion orifices is addressed in U.S. Pat. No. 3,254,482 to Stalego. In this reference a single flow of glass is delivered to various elevations within the spinning head by an interior rotating distributor disk. This disk, which turns at a different rate from the spinning head, delivers molten material both horizontally from a horizontally-oriented portion of its circular surface, and upwardly, along inclined, conical portions of its circular surface. These conical portions have differing angles of inclination thereby delivering the molten flow to different elevations along the inside surface of the outer circumferential wall of the spinner. As depicted, however, the molten feed-stock deposited over the inside surface of the rim-wall is evenly distributed (column 4, lines 60-65); column 5, lines 17-21).
Thus, in all of these prior art reference a focus is maintained on delivering feed-stock to the extrusion orifices on an evenly-distributed basis. Absent from these references is a recognition that the production of extruded fibres from orifices pierced through an annular rim provides zones that are more favourable, and zones that are less favourable to fiber formation.
No proposals have been made to exploit the possibilities of increasing the vertical height of the extrusion rim to provide space for more extrusion orifices, while partitioning the glass flow to exploit the more favourable fiber production zones. Such a procedure, if it could be made to work, would increase the output of a spinning head without having to enlarge the diameter of the head to provide more room on the extrusion rim to carry additional extrusion orifices.
Accordingly, it is an object of this invention to produce a new configuration for a fibre spinning head that provides for differential control over the rates of extrusion of fibres from differing levels of the extrusion rim of the spinning head. Further, the invention provides a means by which the vertical height of the extrusion rim on a fibre spinning head may be extended in order to provide more extrusion orifices and increase the production capacity of a spinning head.
The invention in its general form will first be described, and then its implementation in terms of specific embodiments will be detailed with reference to the drawings following hereafter. These embodiments are intended to demonstrate the principle of the invention, and the manner of its implementation. The invention in its broadest and more specific forms will then be further described, and defined, in each of the individual claims which conclude this Specification.